Fourdrinier papermaking machines currently in use employ a headbox having upper and lower slices that control the jet of stock leaving the headbox. The stock passes over an apron of the lower slice and impinges a forming wire. The forming wire carries the stock through various nips in the forming section so as to dewater the stock and thereby form the paper from the stock. The forming wire in the vicinity of the headbox passes around a breast roll located beneath the headbox and over a forming board. The forming board is positioned in spaced apart relation offset from the apron of the lower slice lip so that after the stock leaves the apron its projectory is such that the jet impinges the wire at a predetermined angle of impingement. In current papermaking machines this angle of impingement is about 5 degrees. The forming wire is known to provide windage as it travels about the breast roll and is known to have fluids entrained in the wire. A fluid shower of water and air passes beneath the underside to the lower slice of the headbox ensuring that there is no build up of paper fibre from the returning wire which could be introduced to the underside of the jet of stock.
There are basically two disadvantages associated with the above described papermaking machine. First the angle of impingement that the stock meets the forming wire tends to produce instabilities and back flow which creates disturbances in the fibres of the stock and results in drainage at the point of impingement causing loss of fine fibres through the wire. Secondly, the pumping action of the wire tends to follow the path of travel of the wire introducing a fluid shower to the underside of the stock which crates further disturbances to the fibres in the underside of the stock.
With respect to the pumping action of the wire, this problem has been recognized previously in Canadian Pat. No. 670,293 which issued Sept. 10, 1963 to Joseph Baxter, Jr. The primary object of this patent is to overcome the difficulties associated with windage from the wire tending to disrupt uniform deposit of stock on the wire. Baxter teaches eliminating the windage problem by introducing a steam chamber between the lower slice lip and the breast roll. The steam chamber produces steam that strips the wire of all windage as the wire passes through the chamber. Baxter further teaches that the condensing of the steam will necessarily produce a corresponding increase in the temperature of the stock resulting in the steam being absorbed. Applicant is not aware of such a steam chamber being used in Fourdrinier type paper machines. The problem with this solution is that the steam under pressure hits the underside of the paper stock destabilizing the stock. Further, the heat generated by the steam chamber heats up the underside of the headbox introducing uncontrollable creep to the lower slice which disturbs the stock jet. Also, the headbox is designed to maintain the temperature of the stock within a predetermined range which will be effected by the heating of the lower slice.